JP4237433B2 - Fluid ejector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to systems and methods for driving electrostatically activated devices using electrical drive signals.
[0002]
[Prior art]
One type of electrostatically triggered device that can use the system and method according to the present invention includes a micromachined fluid ejector. Fluid ejectors have been developed for ink jet recording or printing and other purposes. Inkjet recording devices have many advantages, such as high speed printing, a wide range of choices for ink selection, and the ability to use low cost plain paper that works extremely quietly during recording. A driving method called “drop-on-demand”, which is output only when ink is necessary for recording, is now a normal method. The drop-on-demand driving method eliminates the need to collect ink unnecessary for recording.
[0003]
Fluid ejectors, including those used for ink jet printing, include one or more nozzles, allowing the formation and control of small ink droplets and allowing high resolution. As a result, it is possible to print sharper characters with improved toner resolution. In particular, drop-on-demand ink jet print heads are commonly used in high resolution printers.
[0004]
Drop-on-demand techniques typically use some kind of pulse generator to form and eject droplets. For example, in one type of print head, a chamber having ink nozzles may be attached to a piezoelectric wall that deforms when a voltage is applied. As a result of the deformation, the fluid is pushed out as a droplet from the nozzle orifice. The droplet then strikes the relevant printing surface directly. An example of using such a piezoelectric device as a driving device is disclosed in Japanese Patent Publication No. 2-51734 (JP B-1990-51734).
[0005]
Another type of print head uses bubbles formed by heat pulses to push fluid out of the nozzle. When the bubble collapses, the droplet is separated from the ink source. Japanese Patent Publication No. 61-59911 (JP B-1986-59911) discloses that bubbles are generated using pressure generated by heating ink.
[0006]
Yet another type of drop-on-demand printhead incorporates an electrostatic actuator. This type of printhead uses electrostatic forces to eject ink. Examples of such electrostatic printing heads are described in U.S. Pat. No. 4,520,375 to Kroll and JP-A-02-289351. An ink jet head described in US Pat. No. 4,520,375 is arranged at a position facing a diaphragm (diaphragm) constituting a part of an ink ejection chamber and the diaphragm outside the ink ejection chamber. And an electrostatic actuator including a base plate. The ink jet head ejects ink droplets through nozzles communicating with an ink ejection chamber (chamber) by applying a voltage that varies with time between the vibration plate and the base plate. Thus, the diaphragm and base plate function as capacitors, thereby setting the diaphragm to mechanical motion and allowing fluid to exit in response to the movement of the diaphragm.
[0007]
On the other hand, the ink jet head described in Japanese Patent Application Laid-Open No. 02-289351 bends a diaphragm by applying a voltage to an electrostatic actuator fixed to the diaphragm. As a result, ink is sucked into the ink ejection chamber. Once the voltage is removed, the diaphragm is returned to its pre-bent state and ink is ejected from an ejection chamber that is overfilled with ink.
[0008]
Fluid picking ejectors are not only for printing, but also for multiple chemistry for photoresist and other liquid deposition, chemical and biological sample delivery, chemical reactions in the semiconductor and flat panel display industry Material delivery, DNA sequence handling, drug and biological material delivery for interaction studies and analysis, and deposition of thin thin layers of plastic that can be used as permanent and / or replaceable gaskets in micromachines Can be used for purposes such as
[0009]
[Problems to be solved by the invention]
However, the sub-electric drive method is just one step away from the recent required quality.
[0010]
[Means for Solving the Problems]
The present invention provides a system and method that enables efficient starting of electrostatically driven devices. The present invention also provides a device which is electrostatically start having a driving member and a stationary member, applying a bipolar driving signal to the driving member, a constant potential difference between the stationary member and the drive member A fluid ejector having a drive vibration source for generating an electrostatic field, and a system for electrically driving an electrostatically-started device, the stationary member facing the pressing surface of the drive member An injector nozzle is formed at each end of the drive member, and both ends of the drive member are supported by two or more spring structural elements connected to a substrate, respectively, and a bipolar drive signal is maintained while the stationary member is kept at ground potential by the drive vibration source Is applied to the driving member, the driving member moves toward the stationary member, and the fluid existing between the driving member and the stationary member is sprayed from the injector nozzle. Providing a body injector.
[0011]
The present invention also provides a system and method for electrostatic starting using a constant electric field force.
[0012]
The present invention also provides a system and method for generating increased ejection force for electrostatically initiated fluid ejectors.
[0013]
The present invention also provides an electrostatic starting system and method with reduced potential electrochemical reactions.
[0014]
The present invention also provides an electrostatic starting system and method with reduced conductivity losses.
[0015]
The present invention also provides an electrostatic starting system and method with reduced potential for breakdown.
[0016]
The present invention also provides a system and method for changing the size of the “on-demand” mode of picking in an electrostatically triggered fluid ejector.
[0017]
According to various exemplary embodiments of the system and method according to the present invention, a drive signal is applied to the electrostatically activated device so that the electric field has a constant force. In various exemplary embodiments, the drive signal may be applied by a constant current source. Alternatively, in various other exemplary embodiments, the drive signal may be reduced during its presence.
[0018]
According to various exemplary embodiments of the system and method according to the present invention, the electrostatically initiated device is driven at a speed that reduces the potential effects of electrochemical reactions.
[0019]
According to various embodiments of the system and method according to the present invention, a bipolar drive signal is applied to the electrostatically triggered device so as to reduce the potential effects of electrochemical reactions.
[0020]
According to various embodiments of the system and method according to the present invention, a drive signal having an appropriately high frequency is electrostatically triggered so that the potential for electrochemical reaction and / or electrical breakdown is reduced. To be applied.
[0021]
These and other features and advantages of the present invention are described in, or will be apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to the present invention.
[0022]
Various exemplary embodiments of the systems and methods of the present invention are illustrated in detail below with reference to the accompanying drawings.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
However, it should be understood that the systems and methods of the present invention are applicable to a wide range of devices other than the specific embodiments of fluid ejectors discussed below and general fluid ejectors.
[0024]
In an exemplary embodiment of the system and method according to the present invention, a drive signal is applied to a device that is electrostatically started so that the electric field has a constant force. For example, in a fluid ejector that is electrostatically started, a drive signal is applied to one of a piston and a face plate having a nozzle hole. The injected dielectric fluid is supplied between the piston and the face plate. The drive signal generates an electric field across the fluid between the piston and the faceplate. The electric field electrostatically pulls the piston towards the faceplate, thereby jetting a fluid jet or pinch through the nozzle holes in the faceplate. The electric field has a constant force when the drive signal is from a constant current source or when the drive signal is reduced during one drive pulse.
[0025]
In various embodiments of the systems and methods of the present invention, bipolar drive signals are used. Thus, in various embodiments, a bipolar pulse train of a desired frequency is applied to reduce the possibility of electrochemical reactions. The bipolar drive signal causes the potential on the electrode surface to be periodically reversed. By this inversion, the electrode functions as an anode during a part of the time during which the drive signal is applied, and the electrode functions as a cathode during a part of the time during which the drive signal is applied. Since the reaction at the anode and the reaction at the cathode produce different electrochemical products, the concentration of a particular electrochemical product should interrupt the corresponding reaction and allow the electrochemical product to diffuse into the fluid. Is reduced. This reduces the possibility of exceeding any saturation concentration limit of the electrochemical reaction product in the fluid. As mentioned above, when the saturation concentration limit of any electrochemical reaction is exceeded, there is sufficient thermodynamic driving force for gas aggregation and bubble formation.
[0026]
Electrochemical reactions can also be minimized by reducing the amount of time that the driving electrostatic field is applied. In various embodiments of the systems and methods of the present invention, the time required to drive a fluid ejector is reduced, thereby reducing the time for an electrochemical reaction to occur. Thus, unwanted foam formation is reduced. That is, the amount of unwanted foam formation is proportional to the amount of time that the drive electrostatic field is applied. Therefore, reducing the length of the drive signal reduces the electrochemical reaction that occurs.
[0027]
In various exemplary embodiments, the use of a suitable high frequency drive signal reduces the possibility of electrochemical reactions and / or electrical breakdown. Experiments have shown that the thresholds for fluid breakdown and electrochemical breakdown are related to the frequency of the applied signal. Higher frequency signals increase the threshold at which fluid breakdown occurs. For example, for certain aqueous fluids, the breakdown threshold can be increased by a factor greater than 2 by increasing the frequency of the signal by a factor of 10. The use of higher frequency signals also helps to reduce unwanted electrochemical reactions in the fluid, such as water electrolysis.
[0028]
Water electrolysis occurs under ideal conditions even when the voltage applied between two polar plates is as low as 1.23V. A cathodic reaction occurs at an electrode that is biased or fixed at a relatively more negative potential, producing hydrogen gas. An anodic reaction occurs at an electrode that is biased or fixed at a relatively more positive potential, producing oxygen gas. Thus, electrolysis introduces the possibility of gas dissipation and partial depolarization of the electrode.
[0029]
For example, if the critical saturation amount of either hydrogen or oxygen in the fluid is exceeded, gas bubbles may aggregate and increase in the fluid ejector. Gaseous bubbles affect the dynamics of micropumping from a fluid ejector. Small bubbles in the fluid are unstable and collapse, so that a relatively large amount of energy is released locally by cavitation. This can lead to erosion, such as pitting of polysilicon components in the fluid ejector. This may also cause electrode depolarization, which results in a low steady state potential being applied to the electrode and the electrostatic field being reduced. Since current is drawn by the electrolysis reaction, an increased canceling current is required to maintain the desired electrostatic field. Thus, the efficiency of the fluid ejector is reduced. On the other hand, large bubbles may actually hinder small shot injection by moving fluid away from the nozzle or nozzles or adversely affecting the fluid mechanics of the fluid ejector. Similarly, large bubbles can adversely affect fluid replenishment. The presence of large bubbles is also associated with the risk of reducing the strength of the fluid breaking electric field below that required to eject a small drop of fluid.
[0030]
Other electrochemical reactions are also possible with similar results. For example, the dye molecules of an ink containing a complexed or chelated metal cation, including an organometallic, are typically required to drive a microfabricated fluid ejector. Shows electrochemical reduction or oxidation chemistry. Organic compounds known to be electrochemically active include, for example, hydrocarbons, halogenated hydrocarbons, nitro, amines, saturated carbonyls, unsaturated carbonyls, carboxylates, phenolic compounds, hydroxyl groups, sulfides, Including thiocarbonyl and heterocyclic compounds. If the fluid has a high concentration of additives, such as those described above, electropolymerization may occur, in which case the internal surface of the fluid ejector is coated with the polymerized material.
[0031]
In FIG. 1, an embodiment of an electrostatic starting fluid ejector 100 is shown by way of example only. The electrostatic starter fluid ejector 100 has an unsealed piston 120 that is supported by one or more spring components 122 connected to the substrate 110 on one side of the piston 120. Has been. A face plate 140 having at least one injector nozzle 142 is formed on the other side of the piston 120. A fluid bath 130 is disposed between the face plate 140 and the substrate 110. The fluid bus 130 communicates with a fluid supply source (not shown) through a fluid supply port 112 formed in the substrate 110.
[0032]
The electrostatic starter fluid ejector 100 is applied with a drive signal 152 from a drive signal source 150, and when an electrostatic field E is generated across the fluid in the fluid bus 130 between the piston 120 and the face plate 140. It is started electronically. For example, a voltage can be applied to the piston 120 while keeping the face plate 140 at the ground potential. This potential difference between the face plate 140 and the piston 120 generates an electrostatic field E across the fluid in the fluid bath 130. The electrostatic field E generates an electrostatic attractive force that pulls the piston 120 toward the face plate 140. Due to the movement of the piston 120, the small knob 132 is pushed out of the injector nozzle 142.
[0033]
The drive signal 152 may be used to increase the latitude of fluid breakdown. In very small dimensional areas typical of micro-electromechanical systems (MEMS) or microfabricated devices, such as fluid ejectors, the strength of fluid breakdown is reduced by dimensions critical to failure. It grows according to. This property depends on the fluid considered. In the following description, in order to simplify the description of the system and method according to the present invention, it is assumed that the breakdown strength is constant throughout the dimensions considered.
[0034]
The drive signal 152 may also be applied to the electrode when the injector has a diaphragm instead of the piston 120. A dielectric fluid is contained between the electrode and the diaphragm.
[0035]
In practice, in any case, the specific drive signal 152 used to power the piston 120 or diaphragm and used to push the knob 132 out of the electrostatic starting fluid ejector 100 is Any signal that is effective for this task can be used. However, a constant strength electric field helps to improve the performance of the device without fluid breakdown, especially when the electric field strength is at a maximum. In various embodiments, the systems and methods of the present invention provide a constant strength electric field by directly reducing the applied voltage or by driving the electrostatic starting fluid ejector 100 with a constant current source. .
[0036]
FIG. 2 shows a qualitative example of the drive signal 152 that can be used to bend the piston 120 or the diaphragm and generate the nodule 132. Such a drive signal is generated by the gap between the piston 120 and the face plate 140 or the diaphragm and electrode as the distance between the face plate 140 and the piston 120 or the distance between the diaphragm and the electrode is reduced. A constant electric field E is generated across the gap between the two. The constant electric field E is applied for the length of time necessary to push the knob 132 out of the injector nozzle 142 or to “cock” the diaphragm. Next, in order to allow the spring component 122 to return the piston 120 to its stop position, or to allow the resilient spring force of the diaphragm to return to a position before the diaphragm is bent. The electric field E is cut off. The essence of the method according to the invention is to maintain a constant electric field E through the injection movement of the piston 120 or the “triggering” movement of the diaphragm.
[0037]
In various embodiments of the system and method according to the present invention, an applied voltage that varies with the piston / diaphragm travel or bending function is used to force the piston 120 or diaphragm to a strength lower than the strength of the dielectric breakdown field. You may drive by the fixed electric field E which has thickness. As shown in FIG. 3, closed loop control with a position sensor 160 or other sensing mechanism capable of detecting the amount of movement or bending of the piston / diaphragm may be used. Thus, any known or later developed sensing mechanism may be used, for example, a light-based interferometer, optical sensor, or capacitive sensor. A feedback mechanism 170 is provided to communicate information from the position sensor 160 to a separate control mechanism 180 or drive signal source 150 itself, thereby providing a distance between the face plate 140 and the piston 120 or the diaphragm and electrode. The drive signal 152 is controlled or changed directly as a function of the distance.
[0038]
As shown in FIG. 4, the appropriate timing control 190 may replace the position sensor 160 of FIG. 3 to provide open loop control. Thus, the drive signal 152 is controlled by a time based function or indirectly changed from the distance. Timing control 190 thus provides a time-varying drive signal based on actual performance characteristics in a particular design of fluid ejector 100. Although the timing control 190 is shown as a separate component, it should be understood that the timing control 190 can be incorporated into the drive signal source itself.
[0039]
For fluids where the breakdown strength changes as dimensions critical to breakdown change, the drive signal 152 may be appropriately adjusted to maintain the maximum possible electric field E. . That is, the drive signal 152 may be tuned to have certain characteristics in order to minimize the possibility of electrical breakdown or other electrochemical reactions occurring in the dielectric fluid. First, the electrostatic starter may be driven at a suitable speed. Second, the drive signal may be applied for an appropriate length of time. Third, the drive signal may be a bipolar signal. Fourth, the drive signal may vibrate at a suitably high frequency.
[0040]
Electrostatically initiated devices can be driven at a rate that allows the electrochemical reactions that occur to diffuse and reduce or avoid the adverse effects of these electrochemical reactions. For example, in the case of a fluid ejector, the maximum pinnacle ejection speed is about 40 kHz. Therefore, a small amount of fluid can be ejected every 25 μs while reducing the adverse effect of the electrochemical reaction by the fluid replenishment speed of the fluid ejector.
[0041]
By applying the drive signal for a shorter length of time, potential electrochemical reactions are reduced. For example, if the voltage is applied for a short time, the electrochemical reaction that occurs as a result of the applied voltage has a short time to occur. For example, in a fluid ejector, the minimum amount of time required to eject a small drop of fluid is about 4 μs.
[0042]
A bipolar pulse train having a desired frequency can also be used for the drive signal 152. An exemplary waveform is shown in FIG. Depending on the nature of the electrochemical kinetics, as described above, a bipolar voltage may be applied to minimize the possibility of electrochemical reactions. The magnitude of the effect of the bipolar pulse train depends on the particular fluid used.
[0043]
Experiments have shown that the electrical breakdown threshold of a fluid is related to frequency. More particularly, high frequency signals increase the threshold at which dielectric breakdown occurs by rapidly reversing the polarity of the signal and reducing the time useful for electrochemical reactions at each polarity. The actual relationship between breakdown strength and drive signal frequency depends on the particular fluid considered. For example, in a fluid ejector, the bipolar pulse may be switched about every 0.2 μs while the drive signal is applied for about 4 μs.
[0044]
Advantageously, bipolar pulse trains do not affect device operation because the force applied by the presence of the electric field E depends on the square of the electric field magnitude. FIG. 6 illustrates an electric field of constant strength generated by the bipolar pulse train of FIG.
[0045]
The electronics used to generate the drive signal may be incorporated on a printed wiring board that is mechanically separated from a print head housing comprising a plurality of fluid ejectors or an array of fluid ejectors. In such a case, it is necessary to supply individual electrical leads from the printed wiring board to each fluid ejector. FIG. 7 is a plan view illustrating one embodiment of a printhead assembly 1000 using this method. Thirteen fluid ejectors 1100 are shown in the center. Each fluid ejector 1100 includes a piston 1120 having a spring component 1122. Electrical traces 1200 from a plurality of bond pads 1300 at the edge of the printhead assembly 1000 provide an isolated electrical path to each individual piston 1120 through a spring component 1122. Of course, the printhead assembly 1000 is for illustration purposes only. Many variations are possible, including different sized arrays, etc., having different numbers of rows and columns than those shown.
[0046]
However, this method limits the packing density. For example, because there are design rules that govern the implementation of the bond pad 1300, such as minimum size and space constraints, the maximum mounting density is largely dependent on the shape of the bond pad connection to the individual fluid ejectors 1100. It is determined. This can be a substantial limitation on the size of the array that can be created.
[0047]
An alternative is to use a 2D matrix address technique, which is shown in FIG. In this method, there is one electronic “input” path for columns C1 and C2, and one electronic “output” path for rows R1, R2, R3, and R4. Each fluid ejector 1100 is controlled by a particular column and row being addressed. This method substantially halves the bond pad mounting density, which greatly relaxes the limitations in the foregoing method.
[0048]
A third alternative is to incorporate the main parts of the necessary control electronics into the print head instead of the printed wiring board. When such devices are assembled by silicon-based manufacturing techniques, the electronics can be fabricated on the same silicon chip as the printhead by an integrated process such as Sandia National Lab's IMEMS process. . IMEMS processing is described in US Pat. No. 5,783,340 to Farino et al., US Pat. No. 5,798,283 to Montague et al., Barron et al. et al.), US Pat. No. 5,919,548 to Baron et al., US Pat. No. 5,963,788 to Baron et al., the entire contents of which are hereby incorporated by reference. In this case, the electronics for controlling the address and firing of the individual fluid ejectors 1100 are built into the silicon base, so that the connections for controlling the functions present on the external printed wiring board are controlled. The number may be minimal.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an embodiment of a single fluid ejector electrostatically driven in accordance with the present invention.
FIG. 2 is a graph qualitatively showing an example of a drive signal according to the present invention.
FIG. 3 is a cross-sectional view illustrating an embodiment of a single fluid ejector according to the present invention including a position sensor.
FIG. 4 is a cross-sectional view illustrating an embodiment of a single fluid ejector according to the present invention that includes a timing mechanism.
FIG. 5 is a graph illustrating a waveform of a bipolar pulse train of a drive signal according to the present invention.
6 is a graph qualitatively illustrating a constant intensity electric field generated by the bipolar pulse train of FIG.
FIG. 7 is a plan view illustrating an embodiment of a printhead assembly that can be used with the present invention.
FIG. 8 illustrates a 2D matrix addressing technique for use with the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Fluid ejector, 110 Substrate, 112 Fluid supply port, 120 Piston, 122 Spring component, 130 Fluid bath, 132 Spoiler, 140 Face plate, 142 Injection nozzle, 150 Drive signal source, 152 Drive signal, 160 Sensor, 170 Feedback mechanism, 180 control mechanism, 190 timing control.

Claims (1)

An electrostatically actuated device having a drive member and a stationary member;
The applied to the drive member of the bipolar drive signal, electrical devices that are electrostatically start having a driving vibration source for generating an electrostatic field having a constant potential difference between the stationary member and the drive member A fluid ejector comprising a system for driving
An injector nozzle is formed on the stationary member so as to face the pressing surface of the driving member,
Both ends of the drive member are each supported by two or more spring structural elements connected to the substrate,
A bipolar drive signal is applied to the driving member while the stationary member is kept at the ground potential by the driving vibration source, so that the driving member moves toward the stationary member, and the driving member, the stationary member, A fluid ejector characterized in that a fluid existing between the two is sprayed from the ejector nozzle.

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